Humidity > Influenza Virus

Photo, James Gathany Photo credits: CDC

Photo, James Gathany
Photo credits: CDC

Each year in the winter influenza or “flu” season rolls around and this sickness runs rampant throughout the country. This virus, and many in general, are quite scary because of how easily they can be spread through the air ie. via coughing. Researchers of the National Institute for Occupational Safety and Health (NIOSH of the CDC) have recently linked higher humidity and transmission particle size to more inactivation of influenza (and less spread).

Influenza is an RNA virus that affects mammals and birds causing a small scale pandemic every year in the United States. Viruses tend to mutate very quickly, therefore, it is hard to find a single band-aid to blanket cure this bug. Most people can spread the virus between -1 and 6 days after showing symptoms. Airborne transmission is most likely when this virus appears since many people are in closed quarters attempting to stay warm at home with others during winter.

To test the rate at which influenza stays infectious in different humidities, researchers set up coughing and breathing test dummies in an isolated room. The sneezing dummy released about 4.5×103 virus/liter of air into the room, where 4.6% of that virus was seen to be infectious upon discharge. Of that, upwards of 77.2% of the virus retained infectivity at lower relative humidity (7-23%), while only 14.6% retained infectivity at higher relative humidity of 43%. As a grounding point, average in home humidity during winter is just above 20%, while summer humidity indoors is just below 60%.

Next, the rate of loss of infectivity was measured comparing low and moderate humidity (20% and 45%). Within 15 minutes, 52% of the virus’ infective ability was lost at 45% humidity compared to 20% humidity.

Together these two showed more virus lost its ability to infect new people/etc. at higher relative humidities.

Finally, transmission particle size was measured to see if it had bearing on influenza’s spread and infection at differing humidities. Three particle sizes were used, <1 µm, 1-4 µm, and >4 µm. At the two extremes, <1 & >4 µm, 94% infectivity was seen as lost in the first 15 minutes after coughing virus into the air. However, the 1-4 µm range of particles only showed 29% decrease in infectivity of the virus after 15 minutes. All sizes did, however, show increased loss of infectious ability with more time passed.

It seems as though humidity has great bearing on the inactivation/spreading ability of the influenza virus. At higher humidities, 45% +, the influenza virus showed very little strength in infecting new hosts. This was doubly true when the particle size they rode on was really small or really big.

The best way to minimize your chance to get influenza each year without getting a flu shot?…move to a state with really high humidity in the winter.

John D. Noti, Francoise M. Blachere, Cynthia M. McMillen, William G. Lindsley, Michael L. Kashon, Denzil R. Slaughter, Donald H. Beezhold. High Humidity Leads to Loss of Infectious Influenza Virus from Simulated Coughs. PLoS ONE, 2013.


Influenza vaccine deemed safe for pregnant women

Photo credits: Neville F. Hacker, Joseph C. Gambone, and Calvin J. Hobel

Movies often depict ill pregnant women sacrificing their own well-being to birth a healthy child. However, a research team of Buenos Aires, Argentina has recently proven women at risk of influenza A/H1N1 do not have to make that choice. The MF59 adjuvant A/H1N1 influenza vaccine does not increase the risk of adverse perinatal events.

The influenza pandemic swoops around every year causing more deaths than an expected virus should. In the past, A/H1N1 in pregnant women has been associated with higher hospital admissions, dangerous perinatal outcomes, a rise in perinatal mortality, and early births by about four fold. An H1N1 vaccine using MF59 as the adjuvant (the 2nd punch in a 1,2 combo) was developed in 1997. However, it was seldom prescribed for women nearing birth because of the lack of data detailing the risks. This study attempts to prove that MF59 adjuvant vaccines for H1N1 influenza do not increase risk of malignant perinatal and/or maternal events.

This cross-sectional multi-center study spanned 49 hospitals in the public healthcare sector of Argentina (which handles 15% of live births in all of Argentina). Between September 2010 and May 2011, 30,448 mothers (7,293 vaccinated with H1N1 adjuvant during pregnancy) and 30,769 newborns participated. Mothers were surveyed up to day seven after delivery. Of the vaccinated women, 39.4%, 48.6%, and 10.1% received vaccination during the first, second, and third trimester respectively (1.9% were unknown).

When comparing the vaccinated and non-vaccinated women, it seems those who received the adjuvant had an overall lower incidence of perinatal events. Specifically, in vaccinated women, the following events were seen as reduced:

– Premature birth: 24.6% reduction (P < 0.01)
– Low birth weight: 28.9% reduction (P < 0.01)
– Perinatal mortality: 36.4% reduction (P < 0.01)
– APGAR score < 7: 20% reduction (P = 0.018)

However, maternal complications during pregnancy noted were on par between both groups of women. Analysis of preterm+low birth weight+perinatal mortality rates between the groups led to an odds ration of 0.80 with 95% CI from 0.72 to 0.89 comparing vaccinated to non-vaccinated women.

The A/H1N1 vaccine adjuvant was not linked to any major complications for mother or child during the perinatal period. Perhaps now more women will be able to receive this vaccination when needed without experiencing that surreal moment of “My babies life…or mine?”. (Of course my dramatics here are unnecessary, but the study has proven this vaccine safe)

F. Rubinstein, P. Micone, A. Bonotti, V. Wainer, A. Schwarcz, F. Augustovoski, A. Pichon Riviere, A. Karolinski. Influenza A/H1N1 MF59 adjuvanted vaccine in pregnant women and adverse perinatal outcomes: multicentre study. British Medical Journal, 2013.