The CDC, when it lifted its mask recommendation, stated that- in general- people who have been fully vaccinated do not need to wear masks except in certain situations such as planes,trains and hospitals and contact with the elderly and immunocompromised They further said that one " should consider" wearing a mask if you have a condition that weakens your immune system" or if you lived in an area of the country where the infection rate was high.(High was not defined by the CDC).The "not wearing masks" was heard and little else was remembered and the take home message was the long awaited "take off your masks".
Remembering back to the early days of the pandemic in 2020 we were told that it was a priority to protect the vulnerable which was taken to mean the immunocompromised and the elderly.
Were the elderly ignored in the surprise turn around from the CDC's mask guidance? They did not seemed to be specifically mentioned.
In an earlier blog posting I commented about two studies that addressed the immune status of the elderly following Covid vaccination and I wrote the following:
"Muller et al (1) conducted a cohort study on subjects less than 60 years of age and those over the age of 80 who received the Pfizer vaccine. Specific IgG antibody tiers against SARS-COV-2 spike protein were lower in the elderly and the elderly had no detectable neutralizing antibodies. In the younger group 2.2% had no detectable antibodies."
A large Danish Cohort study (2) compared vaccine effectiveness in health care workers and long term care patients. After the second dose the effectiveness in the patients was 64% ( 95% CI 14-84) while in health care workers the effectiveness was 95% (95% CI 82 -95. The median age of the 39 040 patients was 84 and there were 488 PCR confirmed cases of SARS-COV 2 cases. If this study can be generalized the widely quoted 90 % plus vaccine efficacy does not apply to the elderly. It should be noted that may well represent the worse case in that the eldely in long term care are a less resilient group that 80 years old independently lived in the community. Note also sometimes I am saying effectiveness and sometimes efficacy, they sound alike but in epidemiology they are terms of art and mean different things. More on that below. Also see footnote 1 for explanation of efficacy.
1)Muller,L et al Age-dependent immune response to Biotech/Pfizer BNT 162b2 COVID-19 vaccination Clin infect Dis 2021 Apr 27
2)Moustsen-Helms,IR et al Vaccine effectiveness after 1st and 2 nd dose of the BNT162b2 Covid-19 Vaccine in long term care facility residents and healthcare workers A Danish cohort study. Pre Print from Medrxiv 09 March 2021.
3)Jablonske,K et al The real-life impact of vaccination on covid-19 mortality in Europe and Israel. MedRxiv ( this is a pre print and at the time of publication had not been subject to peer review.
Efficacy refers to the proportional reduction in disease attack rate between ARV and ARU, where ARV is the attack rate of the vaccinated group and ARU is the attack rate in the unvaccinated group.
Risk ratio is the ratio of ARV/ARU
Vaccine efficacy is 1-RR expressed as a percentage.
For example if in a given time frame 100 of unvaccinated get the disease and 5 in the vaccinated group get the disease we have 1-5/100 = .95 or expressed as a percentage of 95%.
To put vaccine efficacy in some context we see that in the 2018-2019 season the flu vaccine has a 29% efficacy .Measles vaccine is about 97% efficacious.