Vaccine-related papers

Fourth vaccine dose improves protection for older people

An initial analysis in Israel indicates that a fourth Pfizer/BioNTech dose improves protection for those over 60. The 4th dose was given about four months after the third, and effects were assessed at least 12 days later. Compared with three doses, and those who had received the 4th less than a week earlier, the fourth dose increased protection against infection two-fold, and protection against severe illness four-fold.

The study included over 1 million people. Differences in behaviour between those who received a fourth or only a third dose can’t be excluded as a potential bias. Further study is needed to determine how long the benefit of a fourth dose lasts. The paper has not yet been peer reviewed.

A news article in Nature discusses the uncertainty about the value of  four or more vaccine doses.

Three doses of CoronaVac broadens the antibody response

A study has found that broadly neutralising memory B cells are produced in some people who have had three CoronaVac vaccine doses. These were not seen in those who only had two vaccine doses. Twenty four of 163 monoclonal antibodies were able to neutralise all current variants of concern. Sera from 60 double-vaxed and 60 triple-vaxed people, none of whom had prior infections, were studied. The paper was published in Nature.

A 2 to 4 month interval between first and second Pfizer doses improves antibody responses

A longer interval between the first and second doses of the Pfizer/BioNTech vaccine improves the immune response. Compared to the standard 3 to 6 week interval, an 8 to 16 week gap improved antibody levels and neutralisation of a range of variants of concern. T cell responses were not substantially different between the two dosing intervals.

The study was relatively small, involving 93 healthcare workers whose median age was 41 and mostly female, so further studies are needed. The paper was published in Nature Immunology.

Effective text messages to encourage vaccinations

A US study examined the type of text messages that are effective at influencing people to get vaccinated. It tested 22 messages about getting the flu vaccine, and included nearly 700,000 patients of Walmart pharmacies. Reminder text messages increased vaccinations by 2%, compared with no messages.

The most effective message consisted of two texts sent three days apart and stated that a vaccine was “waiting for you.”. However, the study supports previous research that multiple reminder messages are more effective, and that communicating that a vaccine is reserved or waiting for you is especially effective. The paper was published in the Proceedings of the National Academy of Sciences.

Non-vaccine-related papers

Results from SARS-CoV-2 challenge trial

Early in the pandemic a challenge trial in the UK was proposed. This involved infecting volunteers with SARS-CoV-2 to study how the infection and symptoms develop in a controlled setting. Results from the clinical trial are now available. Thirty four uninfected people were exposed to the early Wuhan strain of the virus, with 18 becoming infected. Viral load peaked at around 5 days, with viable virus recoverable from the nose and throat for around 10 days after exposure.

The amount of virus being shed did not correlate with severity of Covid symptoms, so asymptomatic people may be as infectious as those with symptoms. Covid-19 symptoms started to appear two to four days after exposure.

The study also demonstrated that twice-weekly rapid tests could reliably diagnose infection before peak viral levels were reached. The median time to detect infections in the throat or nose was around four days after being infected, one to two days after the first positive PCR test.

None of the infected participants developed severe Covid-19 symptoms. The participants were 18 to 29 years old, so the results may not be applicable to older, or younger, people, or those who develop more severe symptoms. The paper has not yet been peer reviewed.

A news article in Nature discusses the clinical trial results.

Poor early interferon response linked to development of more severe Covid symptoms

Further evidence supports the hypothesis that insufficient type I interferon in the respiratory tract soon after infection may enable the virus to spread, leading to pulmonary and systemic inflammation. However, the study also reports that 80% of Covid-related pneumonia do not appear to be due to low type I interferon levels, so there are other factors influencing the development of severe Covid-19. The paper was published in Nature.

Risk assessment of the BA.2 Omicron sub-lineage

The UKHSA has published another technical assessment of variants of concern and under investigation in the UK. This includes an analysis of the BA.2 Omicron sub-lineage, which is showing a faster rate spread than the original Omicron variant (BA.1 sub-lineage). A separate risk assessment of the BA.2 lineage notes that it does not show a greater ability to evade immune responses than BA.1.

The difficulty is assessing Omicron’s virulence

A perspective, published in the New England Journal of Medicine, cautions against making assumptions about the population-level severity of the Omicron variant. It notes that Omicron infections in South Africa were often in people who had been previously infected, so impacts may differ for those with no pre-existing immunity (from prior infection or vaccines). Careful studies are required to better understand the virulence of Omicron.

Theories of Omicron’s origins

Currently there are three main theories for the origin of the Omicron variant, according to an article in Nature. Some of the early stages of its development may have been missed, it could have evolved within an immunocompromised person, or in another species. However, the real origin may not be able to be proven.

In his Science column Derek Lowe also discusses Omicron’s origin and how some of its mutations help evade the immune response.

Transmission between pet hamsters and their owners

A paper, not yet peer reviewed, reports that hamster to human transmission of the Delta variant has occurred at least twice in Hong Kong.

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