This week’s Research Tracker just focuses on evidence of Covid-19 vaccines’ effectiveness and adverse reactions. I’ll send out another Tracker on 1 March that covers other research topics.
The Research Tracker is prepared by Dr Robert Hickson for the Science Media Centre.
Early impacts of vaccinations in Israel
A leaked paper from Pfizer that examines the impacts of vaccinations in Israel is being widely reported because of the claim of a 89.4% reduction in transmission. The paper isn’t yet widely available, but some scientists who have seen it note that some limitations in the study haven’t been picked up by the media.
Zoe McLaren, who has seen the paper, points out in a Twitter thread that the 89.4% figure in the paper is probably an overestimate. This is because more unvaccinated people were tested for infections than vaccinated people.
A news item in Nature discusses the difficulty in establishing whether a vaccine reduces transmission. This is because factors such as lockdowns, physical distancing, mask wearing and changes in behaviour will also affect transmission. Asymptomatic transmission can also be hard to detect. It is expected that some of the vaccines will block transmission, but determining how strongly will be hard to quantify.
A study of vaccinated and unvaccinated health care workers in Israel, published in The Lancet, found that symptomatic cases declined after vaccination. After the first dose of the Pfizer/BioNTech vaccine Covid-19 cases were 47% lower than for unvaccinated health care workers in the first two week after vaccination, and 85% lower after four weeks. Further research is needed to determine effects on asymptomatic infections.
Other research on Israel’s vaccination roll-out, published in the New England Journal of Medicine, analysed vaccine effectiveness between December 20th and February 1st. Comparisons were made between 596,618 vaccinated and matched with 596,618 unvaccinated people (35-62 years old) before and after the second dose.
The estimated vaccine effectiveness in the period starting seven days after the second dose was 92% for documented infection, 94% for symptomatic Covid-19, 87% for hospitalisation, and 92% for severe Covid-19. Results were similar across different age groups. The vaccine appears to be effective against the B.1.1.7 variant. Adverse reactions to the vaccine were not reported in this paper.
Impacts in England and Scotland
An analysis by Public Health England (not peer-reviewed) indicates that the Pfizer/BioNTech vaccine may reduce symptomatic cases by more than 50%. In addition, older vaccinated people were less likely to be hospitalised or die. The report concludes that the level of protection against severe Covid-19 for those over 80 may be greater than 75% after receiving the first dose of the Pfizer vaccine.
Several limitations are recognised in the report. These include the fact that those most at risk will have been vaccinated early on, so greater effects may be seen.
A report from Scotland (not yet peer-reviewed) describes an 85% reduction in hospitalisations 28-34 days after vaccination following the first dose of the Pfizer/BioNTech vaccine, and 94% for the AstraZeneca/Oxford vaccine. This report identifies several caveats that may influence estimates of levels of protection.
Incidence of adverse reactions
An article in Nature discusses research on Covid-19 vaccine safety.
In the UK 8.3 million first doses of the Pfizer/BioNTech vaccine and 6.9 million doses of the AstraZeneca/Oxford vaccines had been given by 14 February. Between 3 and 5 self-reported adverse effects reports per 1,000 doses were received (or 3,000 to 5,000 per million doses). This is in line with expectations. of adverse reactions per 1,000 Self-reporting of adverse reactions lie between
In the US the Pfizer/BioNTech and Moderna vaccines have been calculated to cause non-serious adverse events (such as injection-site pain, headache and fatigue) in about 372 doses out of every million. [Reporting methods differ between the UK and US, so the results aren’t comparable]. More reports of non-serious adverse reactions have been received after the second dose of the Pfizer vaccine than after the first. The mRNA vaccines create a stronger immune reaction than the seasonal flu vaccine, and earlier trials indicated that more people reported transient adverse reactions than for flu shots.
The CDC summarised adverse reactions in the US after the first month of vaccinations. After 13,794,904 vaccine doses 6,994 reports of adverse events were recorded, 90.8% were classified as non-serious and 9.2% as serious.
Limitations in adverse reaction self-reporting schemes are that some people may not report them, while others may report reactions that may not be related to the vaccine. Data from the Phase 3 clinical trails of the vaccines suggest that mild to moderate cases of adverse reactions are being under reported.
The Nature article also notes that the causes of (rare) anaphylactic reactions is uncertain. More than 80% of those who had anaphylaxis after getting either mRNA vaccines had a history of allergies. The US National Institute of Allergy and Infectious Diseases is planning a clinical trial to determine the mechanism(s) for anaphylaxis reactions.
Phase 3 trial data for Johnson & Johnson/Janssen vaccine
Data from Phase 3 trials from Janssen’s Adenovirus 26-based vaccine (requiring only a single dose) have been provided to the FDA. Based on randomised double-blind trials involving 40,000 participants, overall vaccine efficacy 28 days after vaccination was determined to be 66% for moderate to severe cases of Covid-19. The vaccine showed 64% efficacy in South Africa, compared with 68% in Brazil and 72% in the US. No Covid-19 deaths were recorded for those vaccinated.
Adverse side effects were relatively mild and transient, with no cases of anaphylaxis in the trials.
Derek Lowe provides a helpful assessment of some of the data in his Science blog, and discussion about the efficacy of other vaccines. Take away message: things are looking good.
Vaccination plus physical distancing necessary for controlling resurgence
A model based on data from China, published in Nature Human Behaviour, suggests that vaccination alone will not contain further outbreaks or resurgences. Vaccinations need to be combined with physical distancing for a period particularly in areas where population density is medium to high (more than 600 people per square kilometre in their model). Lockdowns can be avoided in these cases. Shorter periods of strong physical distancing requirements can be more effective than longer periods with milder requirements.
Vaccine passports not useful yet
The UK’s Ada Lovelace Institute convened a panel to consider Covid-19 vaccine passports. They conclude such passports are not warranted at this time because the risk of transmission after vaccination remains unknown. However, they also say that this should not stop policy work into developing them.