It is easy to get swamped by all the research on coronavirus. New Zealand’s Science Media Centre is keeping track of much of it so you don’t have to. The Research Tracker is prepared by Dr Robert Hickson for the Science Media Centre New Zealand.

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Vaccine-related papers

Third Pfizer dose effective, at least over the short term

Data from Israel indicates that a third (“booster”) dose of the Pfizer/BioNTech vaccine reduces infection rates by about 10-fold over the short term. This was seen across age groups (16 to over 80 years). Severe illness was also significantly reduced. Those over 60 had more substantial reductions in risk from serious Covid-19 after the booster. Third doses were given at least 5 months after the second dose.

To control for some behavioural changes associated with receiving a booster shot, infection rates within one week of the booster dose (when its effects were likely to be minimal) were compared to those at least 12 days after the booster.

Those under 60 were followed between 28 and 44 days after the booster dose, while over 60s were followed for up to 58 days. The older age group showed greater relative boost in protection than those under 60. How long the immune benefits of the booster shot persist is yet to be determined. The paper has not yet been peer reviewed.

Data provided by Israel to the FDA in support of a third dose was released by the FDA.

Strong effectiveness against hospitalisation for mRNA vaccines for at least 3 months

In a large US study mRNA vaccines were very effective (around 90%) in reducing Covid-related visits to emergency departments, hospitalisations, and intensive care treatment for those aged 50 or older. This level of effectiveness was also the case for groups who were at greater risk -  those over 85, or with chronic medical conditions, and those of African American or Hispanic ancestry.

mRNA vaccine effectiveness remained high for at least 112 days (more than 3 months) after full vaccination.

For the Johnson & Johnson/Janssen vaccine effectiveness (for those going to an emergency department, or being hospitalised) for over 50’s was slightly lower, around 70%. About 40,000 people visiting or admitted to hospitals between January and June were included in the study. The paper was published in The New England Journal of Medicine.

Effectiveness of mixed vaccinations

A US clinical trial found that mixed vaccine doses were safe and resulted in good immune responses. Allergic reactions to a different second dose were similar to those who received two doses of the same vaccine. Neutralising antibody doses were increased more following a different vaccine dose than the same vaccine. However, a broad range of antibody levels were seen for those receiving the same or different second doses.

Three vaccines were involved in the trial - Pfizer/BioNTech, Moderna, and Johnson & Johnson/Janssen. The second dose was given 12 weeks after the first.  

Combining the J&J/Janssen vaccine with a mRNA dose showed large increases in antibody levels relative to a double dose of the latter. Tests were against a D614G variant rather than variants of concern. The trial is continuing. The paper has not yet been peer reviewed.

Moderna effectiveness

A study of 350,000 Moderna-vaccinated people found high levels of effectiveness, which tended to be stable for the subsequent three to six months. Effectiveness against infection was 87%, with effectiveness slightly greater for symptomatic compared with asymptomatic infections.

Effectiveness against hospitalisation was nearly 96%, and 98% against death from Covid-19. Similar results were seen across different age groups, sexes and ethnicities. The Alpha and Epsilon variants were the most common during the study

The study indicated that the vaccine could provide an additional 8 to 33% protective benefit against reinfection for those who have recovered from an earlier infection. The paper has not yet been peer reviewed.

Novavax effectiveness

A Phase 3 trial of the Novavax vaccine found 90% effectiveness against infection and 100% against moderate and severe Covid-19. Several variants of concern and interest were circulating during the trial.

There were no serious safety issues with the vaccine within 28 days after the second dose. Nearly 30,000 people were included in the trial. The paper has not yet been peer reviewed.

Delta spread associated with increasing post-vax infections

A study involving 8.8 million people in New York State concluded that the spread of the Delta variant rather than waning immunity was the main cause of declining vaccine effectiveness against infections. Three vaccines were used in the comparisons – Pfizer/BioNTech, Moderna, and Johnson & Johnson/Janssen - and they all showed similar trends.

Infection rates in vaccinated people increased between May and August as Delta became dominant. This trend was seen in groups that had been vaccinated more recently (March and April) as well as those vaccinated earlier (in January and February).

Moderna provided slightly better protection against infection. The Pfizer/BioNTech vaccine showed the largest percent declines in effectiveness. Effectiveness against hospitalisation remained high for all vaccines over the study period.

There was, though, a tendency for the more recently vaccinated to have slightly higher levels of vaccine effectiveness, suggestive of some degree of waning immunity. The paper has not yet been peer reviewed.

No decline in Pfizer/BioNTech effectiveness against hospitalisation over 6 months

A US study found no decline in effectiveness against hospitalisation over 6 months for the Pfizer/BioNTech vaccine. Vaccination remained effective (93%) against hospitalisation for the Delta variant.

Overall, effectiveness against infection declined from 88%, one month after full vaccination, down to 47% after five months. When just Delta infections were considered, effectiveness was 93% in the first month, declining to 53% four months after full vaccination. The authors conclude that waning effectiveness against infection is due to waning immunity rather than immune avoidance by the Delta variant. The paper was published in The Lancet.

The conflicting conclusions about the cause of waning protection from infection between this and the preceding study may reflect different methodologies and differences in the populations studied.

mRNA vaccines generate immune memory that lasts at least 6 months

Immune memory (memory B and T cells) was created following Pfizer/BioNTech and Moderna vaccines. SARS-CoV-2-specific memory B cells increased between 3 and 6 months after vaccination as circulating antibodies declined. Antibodies produced by these memory cells could bind to Alpha, Beta and Delta variants. Memory CD4+ T cells were stable for 3 to 6 months after vaccination. The paper was published in Science.

Reduced neutralisation of Beta and Gamma variants after vaccination

Variants with the E484K and N501Y/T (seen in Beta and Gamma) mutations are less well neutralised after vaccinations. There is also lower neutralisation of variants with L452R (such as Delta). However, no variants of concern were able to escape immune responses.

Sera from previously infected and then vaccinated people showed  better overall neutralisation ability than sera from uninfected vaccinated people. The authors suggest that a third vaccine dose for those without a previous infection may help provide better protection from variants with the E484K and N501Y/T mutations. The paper was published in Nature.

Increased time between vaccine doses may increase protection from infection …

A Canadian study found that protection from infection increased when the second dose was given later than four weeks after the first. The effect was observed for both mRNA and the AstraZeneca/Oxford vaccines.

Overall protection increased from 82% for doses 3-4 weeks apart to 93% when doses were four months apart. In addition, an AstraZeneca/Oxford dose followed by either a Pfizer/BioNTech or Moderna dose gave a similar level of effectiveness as two mRNA vaccine doses. The paper has not yet been peer reviewed.

… or not

However, a UK study did not find that an increased interval between doses improved protection for the Pfizer/BioNTech vaccine. Comparisons were made between protection from infection when the time between doses was less than and more than six weeks. [Note that the time intervals between doses are different in the Canadian and UK studies]

This study also compared the effectiveness of the Pfizer/BioNTech and AstraZeneca/Oxford vaccines. Both had lower effectiveness against infection of the Delta variant, compared with the Alpha variant. The Pfizer vaccine provided stronger protection against the Delta variant than AstraZeneca’s vaccine. However, the Pfizer/BioNTech vaccine had a more rapid decline in effectiveness over 4-5 months than the AstraZeneca/Oxford vaccine. The paper was published in Nature Medicine.

Benefits of vaccination for pregnant women

Being fully vaccinated reduced the risk of developing severe or critical Covid-19 by about 90%. This was in comparison to unvaccinated or partially vaccinated women. The Delta variant was the dominant strain during the study.

The study involved 10,000 pregnant women, of which only 13% were fully vaccinated. About two thirds of those vaccinated had received the Pfizer/BioNTech vaccine. The paper was published in Obstetrics and Gynecology.

Vaccination reduces infection risk for unvaccinated housemates

A Swedish study found that vaccination reduces the risk of other family members becoming infected. Looking at over 800,000 families, the risk of non-immune members becoming infected declined by between 45 and 97% as the number of family members with immunity to infection increased. Immunity came from natural infection or vaccination. Family sizes were between 2 and 5 people. The paper was published in JAMA Internal Medicine.

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